Gauge control apparatus

ABSTRACT

A gauge control apparatus reduces deviation of an actual plate thickness from a target plate thickness on the delivery side of a rolling mill, in all speed ranges, and produces good products by controlling plate thickness considering changes in the oil film thickness of oil film bearings of backup rolls and the deformation resistance of a rolled material with respect to rolling speeds. The gauge control apparatus computes an oil film thickness compensation value to compensate for increase and decrease of the gap resulting from a change in thickness of the oil film bearing attributable to rolling speeds, an acceleration compensation value to compensate for increase and decrease of plate thickness on the delivery side of the rolling mill resulting from a change in deformation resistance of the rolled material attributable to rolling speeds, and deviation of the predicted plate thickness from the target plate thickness, in consideration of the computed compensation values.

TECHNICAL FIELD

The present invention relates to a gauge control apparatus that controlsa rolled material rolled by a rolling mill to a prescribed target platethickness.

BACKGROUND ART

In a rolling mill which rolls a material to be rolled, the platethickness accuracy on the delivery side of the rolling mill is a greatfactor which has an influence on the quality of products. It is knownthat in such a rolling technique a change in the oil film thickness ofoil film bearings of backup rolls exerts an influence on the platethickness accuracy on the delivery side of the rolling mill. For thisreason, in order to improve the plate thickness accuracy on the deliveryside of the rolling mill, techniques for compensating for a platethickness change on the delivery side of the rolling mill resulting fromthe above-described oil film thickness of the oil film bearings havehitherto been studied.

For example, as conventional arts there have been proposed techniquesfor determining rolling position in consideration of the oil filmthickness of oil film bearings in order to cause the plate thickness onthe delivery side of the rolling mill to approach a target platethickness (refer to Patent Document 1, for example).

-   Patent Document 1: Japanese Patent Laid-Open No. 58-212806

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Although plate thickness control in which the oil film thickness of oilfilm bearings is considered is performed in the technique described inPatent Document 1, no consideration is given to a change in the oil filmthickness or a change in the deformation resistance of a rolled materialdue to rolling speeds during the plate thickness control. For thisreason, this posed the problem that the quality of products worsens whenthe rolling speed changes.

The present invention has been made to solve problems as describedabove, and the object of the invention is to provide a gauge controlapparatus that can reduce a deviation of an actual plate thickness froma target plate thickness on the delivery side of the rolling mill in allspeed ranges and can produce good products by performing plate thicknesscontrol in consideration of changes in the oil film thickness of oilfilm bearings of backup rolls and in the deformation resistance of arolled material with respect to rolling speeds.

Means for Solving the Problems

A gauge control apparatus of a rolling mill of the present invention isa gauge control apparatus which controls a rolled material rolled by arolling mill to a prescribed target plate thickness, and which comprisestop and bottom work rolls which roll the rolled material, top and bottombackup rolls which come into contact with the top and bottom work rollsfrom above and from below and which are each rotatably supported by anoil film bearing, a load measuring device which measures loads appliedto the rolling mill, a gap measuring device which measures a gap formedbetween the top and bottom work rolls, a rolling speed measuring devicewhich measures rolling speeds, and an automatic gauge control devicewhich controls the gap so as to cause a plate thickness of the rolledmaterial on the delivery side of the rolling mill to approach the targetplate thickness on the basis of a predicted plate thickness calculatedby a prescribed plate thickness computing expression and the targetplate thickness. Also, the automatic gauge control device comprises anoil film thickness compensation value computing section which computesan oil film thickness compensation value of the gap relative to rollingspeeds on the basis of measurement results of the rolling speedmeasuring device in order to compensate for an increase and decrease ofthe gap resulting from a change in an oil film thickness of the oil filmbearing ascribed to rolling speeds, an acceleration compensation valuecomputing section which computes an acceleration compensation value of aplate thickness on the delivery side of the rolling mill relative torolling speeds on the basis of measurement results of the rolling speedmeasuring device in order to compensate for an increase and decrease ofa plate thickness on the delivery side of the rolling mill resultingfrom a change in deformation resistance of the rolled material ascribedto rolling speeds, and a deviation computing section which computes adeviation of the predicted plate thickness from the target platethickness on the basis of measurement results of the load measuringdevice and the gap measuring device as well as a mill modulus of therolling mill, the oil film thickness compensation value and theacceleration compensation value, which have been computed.

Effect of the Invention

According to the present invention, by performing plate thicknesscontrol in consideration of changes in the oil film thickness of oilfilm bearings of backup rolls and in the deformation resistance of arolled material with respect to rolling speeds, it is possible to reducea deviation of an actual plate thickness from a target plate thicknesson the delivery side of the rolling mill in all speed ranges and henceit becomes possible to produce good products.

BRIEF OF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a gauge control apparatus in FirstEmbodiment according to the present invention.

FIG. 2 is a diagram showing a rolling mill before acceleration.

FIG. 3 is a diagram showing the rolling mill during acceleration.

FIG. 4 is a diagram showing the relationship between roll speed and theoil film thickness of an oil film bearing.

FIG. 5 is a diagram showing the relationship between deformationvelocity and deformation resistance.

DESCRIPTION OF SYMBOLS

 1 rolled material,  2 top work roll,  3 bottom work roll,  4 top backuproll,  5 bottom backup roll,  6 oil film bearing,  7 lubricating oil,  8shaft,  9 roll surface, 10 shaft, 11 roll surface, 12 load measuringdevice, 13 automatic gauge control device, 14 oil film thicknesscompensation value computing section, 15 bender compensation valuecomputing section, 16 acceleration compensation value computing section,17 deviation computing section

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in more detail with reference tothe accompanying drawings. Incidentally, in each of the drawings, likenumerals refer to like or similar parts and overlaps of description ofthese parts are appropriately simplified or omitted.

FIRST EMBODIMENT

FIG. 1 is a block diagram showing a gauge control apparatus in FirstEmbodiment according to the present invention. FIG. 2 is a diagramshowing a rolling mill before acceleration. FIG. 3 is a diagram showingthe rolling mill during acceleration. FIG. 4 is a diagram showing therelationship between roll speed and the oil film thickness of an oilfilm bearing. FIG. 5 is a diagram showing the relationship betweendeformation velocity and deformation resistance.

In FIGS. 1 to 5, reference numeral 1 denotes a rolled materialconsisting of a metal material rolled by a rolling mill and the like;reference numeral 2 denotes a top work roll; and reference numeral 3denotes a bottom work roll. The rolled material 1 is rolled by the topand bottom work rolls 2 and 3 from above and from below. Referencenumeral 4 denotes a top backup roll which comes into contact with thetop work roll 2 from above; and reference numeral 5 denotes a bottombackup roll which comes into contact with the bottom work roll 3 frombelow. The top and bottom backup rolls 4 and 5 are each rotatablysupported by oil film bearings 6. Incidentally, reference numeral 7denotes a lubricating oil in each of the oil film bearings 6; referencenumeral 8 denotes a shaft of the top backup roll 4; reference numeral 9denotes a roll surface of the top backup roll 4; reference numeral 10denotes a shaft of the bottom backup roll 5; and reference numeral 11denotes a roll surface of the bottom backup roll 5.

The gauge control apparatus shown in FIG. 1 is provided with a hydraulicroll gap control device, a bender pressure control device forcontrolling the crown shape in good condition, a load measuring device12 for measuring loads applied to the rolling mill, a gap measuringdevice which measures a roll gap P formed between the top and bottomwork rolls 2 and 3, a rolling speed measuring device which measuresrolling speeds, i.e., roll speeds, an automatic gauge control device(AGC) 13 and the like.

The automatic gauge control device 13 controls the above-described rollgap P so as to cause a plate thickness of the rolled material 1 on thedelivery side of the rolling mill to approach the above-described targetplate thickness on the basis of a predicted plate thickness calculatedby a prescribed plate thickness computing expression and a prescribedtarget plate thickness. The automatic gauge control device 13 isprovided with, for example, an oil film thickness compensation valuecomputing section 14 which computes an oil film thickness compensationvalue, a bender compensation value computing section 15 which computes abender compensation value, an acceleration compensation value computingsection 16 which computes an acceleration compensation value, and adeviation computing section 17 which computes a deviation of a predictedplate thickness value from a target plate thickness.

The oil film thickness compensation value is intended for compensatingfor an increase and decrease in the roll gap P which are generated whenthe oil film thickness of the oil film bearing 6 changes due to rollingspeeds. The above-described oil film thickness compensation valuecomputing section 14 computes an oil film thickness compensation valueof the roll gap P relative to rolling speeds on the basis of measurementresults of the rolling speed measuring device. The bender compensationvalue is intended for compensating for a difference between loadsapplied to the top and bottom work rolls 2 and 3 and loads applied onthe rolled material 1. The acceleration compensation value is intendedfor compensating for an increase and decrease in a plate thickness onthe delivery side of the rolling mill which occur when the deformationresistance of the rolled material 1 changes due to rolling speeds. Theabove-described acceleration compensation value computing section 16computes an acceleration compensation value of a plate thickness on thedelivery side of the rolling mill relative to rolling speeds on thebasis of measurement results of the rolling speed measuring device.

And the deviation computing section 17 computes a deviation of apredicted plate thickness from a target plate thickness on the basis ofmeasurement results of the load measuring device 12 and the gapmeasuring device as well as a mill modulus of the rolling mill, the oilfilm thickness compensation value, the bender compensation value and theacceleration compensation value, which have been computed.

In the following, specifics of the automatic gauge control device 13will be described.

A predicted plate thickness on the delivery side of the rolling mill hashitherto been found by the following expression:h _(n) =F _(n) /M _(n) +S  (1)

where, h: Plate thickness on the delivery side of the rolling mill, F:Load applied to the rolling mill, M: Modulus of elasticity of the mill(mill modulus), n: Number of mill stands, S: GAP FBK. In expression (1)above, only the load F applied to the rolling mill and the mill modulusM are taken into consideration in the calculation of a predicted platethickness. That is, no consideration was given to the lubricating oil 7of the oil film bearing 6.

In actuality, however, as shown in FIGS. 2 and 3, the lubricating oil 7covers the whole of the shafts 8 and 10 when the roll rotation isaccelerated. That is, the top and bottom backup rolls 4 and 5 move sothat the thickness of the oil films formed around the shafts 8 and 10becomes uniform. For this reason, from the condition shown in FIG. 2 thetop backup roll 4 moves downward and the bottom backup roll 5 movesupward, with the result that the roll gap P becomes closed (see FIG. 3).As a result, during the acceleration of the roll rotation, the load Fapplied to the rolling mill increases compared to the load before theacceleration. On the other hand, the delivery thickness in an actualmaterial is constant regardless of acceleration.

According to expression (1) above, it is recognized that when the loadapplied to the rolling mill increases, with GAP FBK kept constant, theplate thickness h on the delivery side of the rolling mill increases. Inconventional plate thickness control in hot finishing rolling mills,control has been carried out on the basis of expression (1) and,therefore, control for closing the roll gap has been carried out whenthe rolling speed increases. Therefore, this posed the problem that theroll gap is closed although the thickness of an actual material isconstant, with the result that the actual material on the delivery sideof the rolling mill becomes thin.

Hence, in the above-described automatic gauge control device 13, tocompensate for the above-described closing amount of roll gap due toacceleration, the oil film thickness compensation value computingsection 14 is caused to store beforehand a prescribed function forcalculating an oil film thickness compensation value. Incidentally, inthis function, rolling speed is used as a variable and this function isprepared so that an output value increases with increasing rollingspeed. And the deviation computing section 17 calculates a predictedplate thickness by deducting an oil film thickness compensation valueobtained on the basis of measurement results of the rolling speedmeasuring device from a plate thickness obtained on the basis ofmeasurement results of the load measuring device 12 and the gapmeasuring device as well as a mill modulus. As is apparent from theforegoing, it is possible to reduce a difference between a predictedplate thickness and an actual plate thickness on the delivery side ofthe rolling mill.

Concretely, to find a function for deriving the above-described oil filmthickness compensation value, with the roll gap P set in such a marinerthat the load applied to the rolling mill obtains a prescribed value,the rotation number of the backup rolls 4 and 5 is changed from alow-speed rage to a high-speed range and vice versa from a high-speedrange to a low-speed range and a change in load occurring at that timeis measured. Furthermore, by changing the load applied to the rollingmill, loads generated when the rolling speed is accelerated anddecelerated are measured in the same manner as described above (see FIG.4). And the relationship between the roll rotation number (rollingspeed) and the closing amount of roll gap is derived by dividing thefunction of rolling speed and load obtained by the measurement by themill modulus. Incidentally, it is known that the oil film thickness isrelated to the roll speed. Therefore, the above-described function ofthe automatic gauge control device 13 is realized by adopting thederived function described above as an oil film thickness compensationvalue.

In general, in a rolling mill, control for improving crown shape isperformed by use of work roll benders provided in the work rolls 2 and3. Therefore, the load applied to a roll changes due to a change in thework roll bending force. For example, when the work roll bending forceis increased for the purpose of center elongation, the load applied tothe roll decreases because the roll is lifted up. In actuality, however,because also the load of the work roll bender is applied to thematerial, the load applied to the roll differs from the load applied tothe material. Therefore, to compensate for this difference, the bendercompensation value computing section 15 performs compensation by whichthe load generated by a change in the work roll bending force isdeducted from the load applied to the roll.

The automatic gauge control device 13 carries out calculations of apredicted plate thickness on the delivery side of the rolling mill bythe following expressions:F _(B) c=Fb+Fb _(SET)S _(oilc) =S _(oil) +S _(oil0)S _(m)=(F−F _(B) c)/M−S _(oilc)h=+S  (2)where, Fb: Work roll bending force [N], Fb_(sET): Work roll bendingforce setting value [N], F_(B)c: Work roll bending force compensationvalue [mm], S_(oil): Oil film thickness [mm], S_(oil0): Oil filmthickness in zeroing [mm], S_(oilc): Oil film thickness compensationvalue [mm], S_(m): Mill stretch in zeroing [mm], h: Delivery thickness(gauge meter thickness) [mm], M: Mill modulus (mill stiffness) [N/mm].

When the rolling speed is increased, the speed at which the material isreduced in thickness by the rolling mill increases. That is, as shown inFIG. 5, when the rolling speed increases, the strain rate increases anddeformation resistance increases. Because an increase in deformationresistance has the same meaning as an increase in mill modulus, whendeformation resistance increases an actual plate thickness on thedelivery side of the rolling mill becomes small. On the other hand, evenwhen deformation resistance increases, this increase is not reflected inthe actual load and actual roll gap used in expression (1).

That is, although there is no change in a plate thickness on thedelivery side of the rolling mill which is derived using expression (1),an actual plate thickness (a real plate thickness) on the delivery sideof the rolling mill becomes small and a deviation of a real platethickness from a target plate thickness increases. To compensate forthis plate thickness deviation due to rolling speeds, the automaticgauge control device 13 adds a function of rolling speed and roll gapopening as a compensation amount of plate thickness control.

In general, plate thickness control in a rolling mill is performed bycontrolling the roll gap P so that the following equation becomes 0.Δh=h−h(target value)  (3)

where Δh: Plate thickness deviation.

However, as described above, when the rolling speed increases, thestrain rate increases and deformation resistance increases. For thisreason, when the rolling speed increases, an actual plate thickness hbecomes small and actual Δh increases as positive values.

However, because a plate thickness on the delivery side of the rollingmill is larger than a target value in automatic gauge control, theautomatic gauge control device 13 outputs a command to cause the rollgap P to be closed. That is, although an actual plate thickness on thedelivery side of the rolling mill is thinner than a target platethickness, control is performed in such a manner that the platethickness is further reduced.

Incidentally, because the above-described plate thickness variation iscaused by a change in mill stiffness due to rolling speeds, essentially,it is necessary to add compensation by speed to the gauge meter platethickness computing expression. However, because of high rolling speeds,the response may be late if control is performed for compensated gaugemeter plate thickness computations.

Hence, to compensate for the above-described plate thickness variationdue to acceleration, in the automatic gauge control device 13, theacceleration compensation value computing section 16 is caused to storebeforehand a prescribed function f(v) for calculating an accelerationcompensation value. Incidentally, in this function, rolling speed isused as a variable and this function is prepared so that an output valueincreases with increasing rolling speed. And after calculating apredicted plate thickness without using an acceleration compensationvalue, the deviation computing section 17 calculates a plate thicknessdeviation Δh by adding an acceleration compensation value obtained onthe basis of measurement results of the rolling speed measuring deviceto a value obtained by deducting a target plate thickness from thispredicted plate thickness.Δh=h−h(target value)+f(v)  (4)

The automatic gauge control device 13 controls the roll gap P so thatthe plate thickness deviation Δh obtained by expression (4) approaches0.

According to First Embodiment of the present invention, by performingplate thickness control in consideration of changes in the oil filmthickness of the oil film bearings 6 of the backup rolls 4 and 5 and inthe deformation resistance of the rolled material 1 due to rollingspeeds, it is possible to reduce a deviation of an actual platethickness from a target plate thickness on the delivery side of therolling mill in all speed ranges and hence it becomes possible toproduce good products.

That is, by using oil film compensation and acceleration compensation incombination, it is possible to constantly realize optimum platethickness control regardless of whether high-speed rolling or low-speedrolling is performed and hence it becomes possible to improve platethickness accuracy.

INDUSTRIAL APPLICABILITY

As described above, according to the gauge control apparatus related tothe present invention, it becomes possible to perform optimum platethickness control in all speed ranges by using oil film compensation andacceleration compensation in combination. Therefore, regardless ofwhether high-speed rolling or low-speed rolling is performed, it ispossible to apply the present invention to automatic gauge control (AGC)in both hot rolling and cold rolling.

1. A gauge control apparatus which controls a rolled material rolled bya rolling mill to target plate thickness, comprising: top and bottomwork rolls which roll the rolled material; top and bottom backup rollswhich respectively contact the top and bottom work rolls from above andfrom below and which are each rotatably supported by an oil filmbearing; a load measuring device which measures loads applied to therolling mill; a gap measuring device which measures a gap between thetop and bottom work rolls; a rolling speed measuring device whichmeasures rolling speeds; and an automatic gauge control device whichcontrols the gap to cause plate thickness of the rolled material on adelivery side of the rolling mill to approach the target plate thicknessbased on a predicted plate thickness calculated using a plate thicknesscomputing expression and the target plate thickness, the automatic gaugecontrol device comprising: an oil film thickness compensation valuecomputing section which computes an oil film thickness compensationvalue of the gap relative to rolling speeds based on measurement resultsof the rolling speed measuring device to compensate for increase anddecrease of the gap resulting from a change in oil film thicknesses ofthe oil film bearings, which is attributable to rolling speeds, anacceleration compensation value computing section which computes anacceleration compensation value of plate thickness on the delivery sideof the rolling mill relative to rolling speeds based on measurementresults of the rolling speed measuring device to compensate for increaseand decrease of plate thickness on the delivery side of the rolling millresulting from a change in deformation resistance of the rolled materialwhich is attributable to rolling speeds, and a deviation computingsection which computes deviation of the predicted plate thickness fromthe target plate thickness based on measurement results of the loadmeasuring device and the gap measuring device, and a mill modulus of therolling mill, the oil film thickness compensation value, and theacceleration compensation value, which have been computed.
 2. The gaugecontrol apparatus according to claim 1, wherein the oil thicknesscompensation value is calculated using a function in which an outputvalue increases with increasing rolling speed; and the deviationcomputing section calculates the predicted plate thickness bysubtracting the oil film thickness compensation value, obtained on basedmeasurement results of the rolling speed measuring device, from platethickness, obtained based on measurement results of the load measuringdevice and the gap measuring device, and the mill modulus of the rollingmill.
 3. The gauge control apparatus according to claim 1, wherein theacceleration compensation value is calculated using a function in whichan output value increases with increasing rolling speed; and thedeviation computing section calculates deviation of the predicted platethickness from the target plate thickness by adding the accelerationcompensation value, obtained based on measurement results of the rollingspeed measuring device, to a value obtained by subtracting the targetplate thickness from the predicted plate thickness.
 4. The gauge controlapparatus according to claim 2, wherein the acceleration compensationvalue is calculated using a function in which an output value increaseswith increasing rolling speed; and the deviation computing sectioncalculates deviation of the predicted plate thickness from the targetplate thickness by adding the acceleration compensation value, obtainedbased on measurement results of the rolling speed measuring device, to avalue obtained by subtracting the target plate thickness from thepredicted plate thickness.